In order to control a driving motor, which is used for drive of for example an automobile, a robot, etc, it is necessary to detect a rotation angle of a rotor with a high degree of accuracy. A resolver has widely been used as an apparatus for detecting a rotation angle of the rotor. The resolver, which has currently been used, mainly has a stationary unit and a rotation unit, and irregularity, deviation, etc. of the stationary unit may be utilized to detect a rotation angle (see for example Japanese Patent Provisional Publication No. 2009-128133 (Patent Document 1) and Japanese Patent Provisional Publication No. 2008-29070 (Patent Document 2)).
Patent Document 1 shows an art of a resolver, which comprises a plurality of magnetic cores with wound wires, a stator having a plurality of members with wound wires, which are provided around the respective magnetic cores, and a rotor provided rotatably relative to the stator, at least one of the plurality of members with would wires being a sheet-shaped coil in which a conductive material is patterned in a spiral manner on a sheet, and at least a portion of the surface of the sheet on which the conductive material is pattern-formed, or the back surface thereof facing a side surface of the above0mentioned magnetic cores with would wires, and also shows a structure of the rotor having four projections and an eccentric structure relative to an axis.
Patent Document 2 shows an art of a structure in which the inner surface of a curved gap formation plate, which is provided on the inner surface of a ring-shaped rotor plate, is placed to face a plurality of stator-wound wires on a ring-shaped stator plate, to obtain angle signals varying in a sine wave shape.